My blackberry curve 8520 wont delete my texts?

I have it set to delete after 15 days...
I still have texts from February, lol.
I have changed the 15 days to a month then changed it back but it didn't work, and i've also waited 15 days (obviously) but nope... they didn't delete.
I don't want to be stuck with texts from February and theres no delete all button.
Can someone help me?
Thanks :)

u can click on a text then click menu then click delete prior...

go to very top of ur sms screen. make sure the day is highlighted. ex: Mon, May 3, 2010. press the blackberry and then click delete prior.

this works if u can understand how i have it worded :D